Electromagnetic device



E. J. MURPHY.

ELECTROMAGNETIC DEVICE.

APPLICATION FILED FEB. 15, Hill.

153525307, PatentedSept. 7, 1920.

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/ ///ly A tforney E. J. MURPHY.

ELECTROMAGNETIC DEVICE.

APPLHIQTIUN FILED FEB. 15, 19H.

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ELECTROMAGNETIC DEVICE.

APPLICATION FILED r:a.|5,|9|1.

1 ,352,307 Patented Sept. 7, 1920.

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Wl'finesses: Dive/760i" i [aw/n J. Murphy,

y Wttorney E. J. MURPHY.

ELECTROMAGNETIC DEVICE.

APPLICATION FILED FEB..I5. [9|].

1,352,307, Patented Sept. 7, 1920.

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Witnessesln Pen 60/" EdW/h JMu/"phy UNITED STATES EDWIN J. MURPHY, OFSCHENECTADY, NEW YORK. ASSIGNOR. TO GENERAL ELECTRIC PATENT OFFICE,

COMPANY, A CORPORATION OF NEW YORK.

ELECTROMAGNETIC DEVICE.

Specification of Letters Patent.

Application filed February 15, 1911. Serial No. 608,652.

To all when: it may concern:

lie it known that I, Eowm J. MURPHY, a citizen of the United States,residin at Schenectady, county of Schenectady, btate of New York, haveinvented certain new and useful Improvements in Electromagnetic Devices,of which the following is a specification. 1

This invention relates to the control. of electric circuits and has .forits object the provision ofmeans whereby an electric circuit may beeffectively controlled in a re-' liable, simple and eilicient manner.

One of the objects of myinvention is to provide an improvedelectromagnetic device which is inactive when the excitation is high andbecomes active upon a lower excitation. In one embodiment of Ininvention 1 provide an electromagnet wit 11 a movable;

current, and therefore the ma netic flux is sufliciently small so thatare a'tivel large portion of the total flux is shunted t irou h this ironpath. Under these conditions 1; e force across the shunted gap isdiminished. When the current, and therefore the flux, is

correspox'ulingly higher, the shunt becomes more highly magnetized andceases to short circuit so large a proportion of the flux and -thereforethe'flux across the air gap which is shunted, and hence the force ISrelatively increased. With the arrangement above described it is obviousthat the distribution of the flux in the two air gaps, one of which isshunted by a path of limited magnetic carrying capacity, :raries betweenwide limits whenthe total flux is changed. This variation can be furtherincreased by making the iron path in series with the other ga of smallmagnetic carrying capacity. his electromagnetic device may also beprovided with means for producing a time la of the flux through themagnetic shunt, tius rendering it less active and hence the shunted airgap more active for a short time when the electromagnet is firstenergized. While myinvention is capable f various applications inelectric circuits I have found'it to be particularly well adapted for;use in the control of electric motors. In the control of electric motorsit is common to insert a resistance at starting so as to reduce thecurrent through the motor armature. It is also common to vary the speedof a motor by varying the amount of resistance in the armature cir cuit.Every time a portion orsection of resistance is cut out of circuit thecurrent rises. This rise in current is only temporary since the increasein current causes the motor to increase in speed and the counterelectromotive force of the motor is thereby increased and the currentreduced. In the starting of a motor, as well as in the controlling ofits speed, it is often essential that provision be made for preventingthe resistance from being cut out too rapidly so as to cause the currentto rise to a dangerous value. In some types of motor control, theresistance sections are cut out of circuit by electromagnetic switcheswhich operate automatically in sequence. In systems of control of thischaracter it is common to provide means whereby the closure of theswitches 18 under the controlof the current in the motor circuit. Thisis commonly known as-cnrrent [limit control; The means for preventingthe closure of theswitches while the current is temporarily higher thannormal has in some cases taken e form of an overload or throttle magnetwhich controls the actu db. ing circuit of each switch and prevents'it'Patented Sept. 7, 1920.

from being energized when the current is too high. In other cases anoverload device is provided in connection with each switch to preventthe energization of the actuating winding of asucceeding switch. Suchairrangements as these involve the use of shunt windings of fine wire,interlocking switches, etc, which adds to the cost and complication ofthe equipment.

In applying my invention to motor control I provide 'an electromagnethaving a winding which is energized by the'motor current, and a switchmember actuated thereby which cuts out a section of resistance. Thiswinding is capable of carrying the motor current upon one of thetemporary rushes of current incident to the cutting out of a section ofresistance. The ar member is held open by a ma netic force which opposesthe magnetic orce which tends to close it. As the current decreases theforce tending to hold it open decreases until finally when the currentreaches a predetermined value, the switch is released and is closed bythe other force.

I have found that by the use of means for producing a time lag of theflux through the magnetic shunt, I am able to improve the operation ofthe switch and obtain the desired current limit control with a very muchsmaller rise of the current above its normal trippin point than would berequired if the means or producin the time lag were not employed. One 0the methods by which the time lag may be, accomplished, 'is to rovide ashort circuit around the magnetic shunt which keeps the shunt inactivefor a short time after the current is thrown on and then permits it toact. The same general result may, in a measure, be obtained by rovidingmeans for lagging the magnetic ux at some other point, as, for instance,at the main air ga of the switch. This may be accomplished yconstructingthe upper member which supports the switch core of large crosssection'and making it of'a. material of high electrical conductivity,such as cop er or brass. In practice, I prefer to emp 0 both of thesefeatures in the same switc My invention includes as an additionalfeature means whereby any switch or number of switches constructed asabove described may be held open under the control of the operator evenwhen the current has fallen to the predetermined closing value, so thatthe closure of the switch or switches is not only controlled by thecurrent but is also controlled b the operator.

Other objects an purposes of myinvention will appear in the course ofthe following specification in which I have shown my invention embodiedin concrete form for purposes of illustration.

Referring to the drawings which show mv invention embodiedin variousforms, Figure 1 shows one of my electromagnetic switches complete; Fig.2 1s a section on the line 2-2 of Fig. 1; *ig. 3 is a section on theline 3--3 of Fig. 1; Fig. 4 shows my control-system; Fig. 5 showsanother form of electromagnetic switch; Fig. 6 shows a system ofcontrolincludin a number of switches of the type shown in lhg. 5 Figs. 7, 8, 9,and 10 are various modificat ons of my electromagnetic switch; and Figs.11 and 12 are still further modifications of the switch.

Referring first to Fig. 1, 10 represents an insulating base of slate orsoapstone upon which is mounted a fixed contact 11 cooperating with amovable contact 12. An electromagnet' 13 having a core 14 of magneticmaterial is mounted upon the base below the contacts. The core 14 passesthrough a plate 14' of non-magnetic material, preferably of brass orcopper for the reasons above specified. This is secured to the base, anda lug 15 forms a part of the brass plate. One end of the coil wmding isconnected to lug 15' and the other end is connected to ter- .m1nal 13f,connection being made to these terminals and to contact 11 from the backof the slatebase as shown. Coiiperating with the magnetic core 14 is amember 15 of magnetic material pivoted at 16 to an'iron su port 17.,This sup art 17 is secured to t e brass plate 14', an is in conductiverelation with the brass frame and terminal block. The switch member isin the form of a bell crank lever having a bracket 18 pivoted at i 19'for carrying the movable contact 12. This bracket 18 is movable on thepivot 19 to a small extent b reason of the compres- -sion spring 20which forces the rojecting end 21 against the bracket. ThlS ermits thecontact member 12 to move su ciently when it is forced against themember 11 to furnish a wiping contact. The contact 12 is electricall.inember 1i by'a copper cable 21. cured to the member 15 is a bar 22 ofmagnetic material which projects downward so as to cooperate with thepolepiece 23 of the magnet. his polepiece is in engagement with the core14 so as to form part of the magnetic circuit through thecore. Themember 15, together with the bar 22, constitute in effeet a singlearmature for the magnet comprisingthe core 14 and the polepiece 23, andthe weight is so distributed that the parts normally rest in thepositionshown in Fig. 1. In this position the bar rests against the brass nut 24which holds the armature bar 22 out of engagementwith the pole iece 23so as to leave a small air gap at 25. he nut 24 is adjustable on screw26 so as to va the air gap 25 and the spring 27 acts to he] the nut inan position to which it is turned. The switc 1 member thus has twoarmature portions 22 and 15, the former coiiperatiug with the polepiece23 while the latter cooperates with the core 14;

In order. to produce a ma netic force between the polepiece 23 anarmature. 22 across the air gap 25 sufiicient to hold the switch fromclosing against the pull of the 'core 14 upon the armature portion 15when the current is high and release it when it is low, I provide.magnetic element 28 which acts as a shunt for the flux of the magnet.This element 28 is in shunt to the air gap 25 and is of limited magneticcarr 'ng capacity.

It is secured at'one end to the rass plate 14' and at the other end tothe polepiece 23'. The flux of the magnet thus has two paths, one fromthe core 14 throng shunt 28, iron support 17, arm 15, and air gap 16,

connected with the supgprting arallel .short circuit around the shunt.

while the other path is through polepiece 23, across the air gap 25,armature 22, arm 15, and air gap 16". The shunt 28 is shown wide so asto act as a screen. When the current through the magnet winding isrelativel low and the flux of the magnet correspomiingly low, themagnetic element 28 shunts a relatively large portion of the flux aroundthe gap 25 and makes the gap relativel inactive. When the flux is high,due

higher current, the shunt becomes more highly magnetized and no longershunts so large a portion of the flux. This causes the air gap 25 tobecome more active. In other Words, when the winding 13 is energized ata relatively high current, two opposing ma netic forces are exerted uponthe switai member, the stronger or moreefiective force acting onarmature22 tending to keep the switch open and the weaker or lesseffective force acting upon the armature 15 tending to close it. Whenthe current is diminished the stronger magnetic force is weakened by themagnetic shuntpath which isnow less highly magnetized. While the fluxacross the gap 16 decreases as the total flux decreases, the flux acrossthe gap 25 decreases much more rapidly, since the flux is appreachingthe point at which the shunt will carry a very much reater proportion ofthe total flux. lVhen the current falls to a predetermined value, thepull on the armature l5 overcomes the pull on the armature 22 and theswitch is closed. As shown in the drawings, the armature 22 is longerthan the arm 15 so as to give it a greater leverage. The magnetic forceupon the armature 22 tending to hold the switch open may thus beconsiderably less than that upon the armature l5 tending to close it andstill the switch will be held open By increasing the air gap 2:) thepoint at which the armature released may be adjusted. The current in thewindin 13 in rising to the higher value at whichthe switch is held openby the armature portion 22, passes through the lower value at which theswitch will close. The closin of the switch at this point may be guardeagainst under some conditions by suitable design and proportioning ofthe parts, but the operation may be greatly improved, as before stated,by providing means for introducing a time lag.

One way of accomplishing this I have shown in the drawings. Thisconsists of a As shown in the drawings, this consists of a ring or bandof coppcr'or similar non-magnetic material'of low electrical resistancesurrounding the shunt. A transient current of high value is thus inducedin the ring which temporarily opposes the increase of the flux in theshunt path; that is, it renders the shunt temporarily inactive, therebycausin the air gap 25 to be sufficiently active to ho d the mains a, a',current will pass magnet winding the switch will be held'" openand whenthe current falls to a predetermined value it ,.will be closed. T herelative value of the forces tending to attract the armature 15 towardthe end of the core 14 andfthe armature 22 against the end of thepolepiece 23 may be adjusted by varying the relative areas of the airgaps at these two points, in accordance with well known laws ofelectromagnetic action.

In Fig. 4'1 have shown a plurality of these electromagnetic switchesarranged to be operated successively to cut resistance out of the motorcircuit. Referring to this figure, which ispurely dia rammatic, Arepresents thearmature and F the shunt field of an electric motor. Thestarting resistance of this motor is composed of sections divided intortwo groups, R and R constituting one group, while R constitucs the eachswitch is connected with the movable switch -member ofthe nextsucceeding switch at the terminal 15, thereby also connectin with theactuating coil of the next sucoee ing switch. It -will also be notedthat the actuating coil in each case has one terminal connected with itsown movable switch member, while the. other terminal is connected with asection of resistance. Taking the switches in their order, the firstmagnet winding is connected with a resist ance of one group while thenext winding is connected with a resistance in the other group and soon, the successive coils being alternately connected with resistancesections of the two groups.

The operation of the system will be as 'follows: When volta e is a pliedto the rom the main a through the armature A, resistance R", windin 13,resistance R and R back to the main (1. This causes the motor to startwith the resistance in circuit. The switch member 12 will not, however,be closed because the current is momentarily hi h. As the motor armaturerises in speed, t e current will fall to the predetermined safe valuedue to the rise in counter clectromotive force of the motor and theswitch S will close. When this closes, a section of resistance R will beshort circuited and at the same time the winding 13 will be ener-,gized. The direction of current will now we as follows from the main a,armature 12, 11, winding 13', resistance back to main (1.

short circuitifig of the resistance R increases thecurrent momentarilyso that the switch S will not close until the motor' speeds up to reducethe current: When the current again falls to the predetermined value theswitch S will close. The closing of this switch short-circuits theresistance R and at the same time energizes thenext succeeding winding13 It likewise short circuits the winding 13 so as to permit the switchS to open. The direction of ourrent will now be as follows: from themain a, armature A, winding 13', contact 11', i2", winding 13,resistance R, back to main (1. Again the current is increased by thecutting out of the resistance seetion-R and when it falls to thepredetermined value'by the further increase of the speed of themetorswitch S will close, th818by-SllOlt*GiI' cuiting the winding 13' andthe'resistance i R Switch S now opens-and the motor-is connecteddirectly acrossthe'line -in series" with the winding 13 switch S nowbeing;'

the only switch whicln is closedj Upon failure of voltage dueton-anycause -the switch S will open and can notibe again closed until theother switches are closed in the order stated. It will be seen thatthisprovides acurrent limitSystem ofi'control in which each switch has-a Slllglfi series" winding and a single switch member, all interlockingswitches and auxiliary coilsbeing. dispensedwith. It is obvious," of

course, that'my invention is in no sense limited in its applicatio'ii'tothe particular motor control system described'since it ma'y beemployed in other systems of control, and in :factds notsliimited to usein control systems but :is adapted for wide application in theelectrical art; 7

lVhatever the character of th'e system in which my switches are*employedit is in some casesdesirable that means be'provided" whereby theclosingof the switches may be regulated by the operator; that "is, it isdesirable to have. control by the 'operatorr'in addition to thecurrent':.liii1it control. This result I may accomplish in various ways.Iii-Fig.5 I have shown one method of doing this consistin of anadditional winding-29'- which holds t e switch"open whilethe'coil isenergized. In this case the coil is mounted upon the shunt 28 so thatwhen the coil is energized the shunt 27' is magnetized in the opposite:direction to that in whichitds en-" ergized by the main winding i andthe flux across the air gap- 251 will bra-increased to such apointthatthe switch-will he held" open undor allconrlitions so long asthe coil is energized The adjustmentof' the air gap 25 in this case ismade ina slightlydifi ferent manner from that above descr bed an thatthe-air gap is varied-"by screwing the iron-nut 24' toward and from thearmature on astationaryserew. This" has the advan- -tage zthat thearmature always goes back to i P position the'coil '29will befienergizedand the-switch T- wili close. As before, the closing of theswitc'hT"ener izes the winding off the'switch T' and this latter switchwillfclose-whendhe c'l'irr'ent'fiills to a predetermined-value and thecontroller "has been moved to the next position. In this way, whenthef'conttbller is movedto the fourth position the winding 29 will beenergized andthe'sWitch T will be closed, thus throwingithe'rnoteriarmature across the line in series withthe' winding ofswitch T inFig.7 l haveshown'another means for holding theswitch in open positionconsistingof awindihg3O "which'acts upon a pivoted armature 31. Thisarmature is connected tow-linlr 32 pivotedto the armature 22at "33. Thearrangementis such that when the windinga30 is energized, the armature'22wi'll be held against'its stopand the switch will be-' held open.

In Figu 8 1 ha ve shown still another method of accomplishing thisresult. In'thi's case'the-shnnt eoilB l is'arranged below the main' series coil. When winding 341s en- "ergized "it will 'eause th'e*flux'acrossthe airgapft'o be increased and hold the switch open so king'- as the"winding"34 is energized. VVh'en thewindingil l is deenergized it willclose as before."

In FigJ9d have shown the holding coil mounted on the end of p olepiece36 so as to hold the switch open when the coil is ener ize'd.

i Fig; 10, coil 37' is mounted parallel with thesh'unt and a polepiece38 is arranged' adj'acentarmature'22 so as to hold it as before."

'In Fig. -"11 I haveshown a somewhat dif ferent arrangement cf theswitch. In this case there is a polepiece -on' each side of the magnet39 and the-'switch-inember 40 is pivoted centi-ally'ofi=the magnet.Polepiece 41' forms the endof an' iron piece 41 of angular sha e securedto the core fl2'ofthe magnet: e other polepiece 43 is connected totheangular olepieceand spaced therefrom by a block of brass 44.- whichfurnishes an air gap, Shunt 45in this caseco'nnects the core encirclingstrip-46 or thc purposefheretofore, described. In this case the two]aths for the flux are from the core 42'through shunt 455 and alsothrough the switch member 40 across the gap 17 to polepicce If thecurrent in the ,winding is highla large proportion of the flux'is lfioreedjaoross the air gap 47 and the switch memberis held in theposition shown. When the current diminishes the switch member will bereleased and attracted by the polepiece 4:1. The air gap 44 in thisswitch is the equivalent of the air gap between the armature 15 and thecore 1 1 in Fig. 1 and is desirable in some cases. Without this air gapthere would be a ermanently closed magnetic circuit.

11 some cases it is advantageous to decrease the cross section of thelI'OIl path in series with polepiece 41 thus making the iron portion ofthe path of limited ma etic carrying capacity. For instance, i the ironat 41' is reduced so as to decrease its magnetic carrying capacity, theresult will be that the flux across the gap 42' will be relativelysmaller with large exciting currents in the coil 39 and Wlll berelatively larger with small exciting currents in the coil. Since theoperation of the device depends upon the relative value of the opposingforces, due to the flux across the two air gaps, it is obvious that thisarrangement will increase the range of operation.

In Fig. 12 I have shown still another form of switch in which a magnetof the solenoid type is employed. In this case the movable core 48 has aU-shaped member 49 secured to its lower end so as to form a olepiece 5Oextendin around the magnet.

he core is supports; at the bottom by an adjusting screw 51 and theswitch member 52 is connected with the upper end of the core. An ironring 53 is mounted below the coil and a copper ring 54 is below the ironring. The portion 55 of the U-shaped 'member acts as a magnetic shunt.When the current is high in the coil, the flux is forced across the airgap 56, which holds the core in the down position. When the currentdiminishes, the flux across the air gap 56 diminishes and the core ispulled upward to close' the switch by the attraction between the ironplate 57- and the polepiece 50 and core 48.

While I have described my invention as embodied in various concreteforms for puroses-of illustration, it should be understood that I do notlimit my invention thereto, nor do I limit my invention to theparticular connections or mode of operation therein described, sincevarious modifications thereof will suggest themselves to those skilledin the art without departing 1 from the spirit of myinvention, the scopeof which is set forth 1n the annexed claims. What I claim as new, anddesire to secure Iiettersfatent of the United States, is,-

A controllingdevice for electric cirg'ci iftscornprising apiv'otedswitch member 'li aving' aniarmature portion on each side ,of'thepivohan' electromagnet acting on one "o'fsaid armature portions to closethe switch "and onfthe otheriarmature portion to hold it "epeaanaamagnetic shunt to said holding portion which approaches saturation whenthe exciting current of the magnet is above a predetermined value andcauses the holding force to predominate until the current is decreasedto the predetermined value.

2. A controlling device for electric circuits comprising a switch memberhaving two armature portions, an electromagnet cooperating with one ofsaid armature portions to close the switch and with the other armatureportion to hold it open, a magnetic shunt to said holdin portion whichapproaches saturation w an the exciting current of the magnet is above apredetermined value and causes the holding force to predominate untilthe exciting currcnt is decreased to the predetermined value, and acopper sleeve surrounding said magnetic shunt for retarding the changesin flux density therein.

3. An electromagnetic device comprising an electromagnet, a magneticcircuit therefor including an air gap, a magnetic element of limitedmagnetic carrying capacity in shunt to said air gap which approachessaturation at relatively high excitation of the magnet and therebycauses the air gap to become magnetically active, and a short circuitednon-magnetic conductor of low electrical resistance surrounding saidelement for retarding the changes in fiux density therein.

4. A controlling device for electric circuits comprising anelectromagnet having a stationary core, a switch member having anarmature portion cooperating with one end of said core to close theswitch and a second armature portion cooperating with the other end ofthe core across an air gap to hold it open, and a magnetic shunt which"approaches saturation when the winding of the electromagnet isenergized above a predetermined value connected across the air c Acontrolling device for electric circuits comprising a pivoted switchmember having an armature portion on each side of the pivot, anelectromagnet acting on one of said armature portions to move the switchmember to closed position and onthe other armature portion to hold it in0 en osition and means whereby the holding orce predominates when theexciting current of the magnet is above a predetermined value and theclosing force predominates toclose the switch when the current isdecreased to said value.

6. A controlling device for electric circuits comprising anelectromagnet having a stationary core, a switch member havin anarmature portion acted upon by the sai core to close the switch and asecond armature portion acted upon by the core to hold the switch inopen position and means whereby the holding force predominates thecurrent is decreased to said value.

EDWIN J. MURPHY.

Witnesses:

BENJAMIN B. HULL, HELEN Omronn.

